Internet in outer space

NASA's Curiosity has now landed and begun beaming back pictures from the surface of Mars. But how exactly does the Internet work in outer space? Today I'll break down the publicly available details. We'll start with the Rover itself and work backwards from there.

The first thing any device needs is, of course, power. The Mars Science Laboratory Fact Sheet reports that Curiosity is powered by a "U.S. Department of Energy radioisotope power generator." This nuclear device has enough power to last for a full Mars year, or 687 Earth days! It's essentially a really big battery, one that can survive the trip out through Earth's atmosphere, months in deep space, and then landing on Mars.

Once there is power, according to the OSI model the next step is a data link. The fact sheet indicates that a radio transmitter is part of the rover, and that the radio signal will be received by the existing satellites orbiting Mars. Those satellites will then relay the message on to the "Deep Space Network" of satellites which NASA uses to communicate to objects in outer space. This is actually where all communications occur with Curiosity, so it's not actually "on the Internet." Instead, it's more like two walkie-talkies talking to each other.

The NASA Deep Space Network - or DSN - is an international network of antennas that supports interplanetary spacecraft missions and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected Earth-orbiting missions.

The DSN currently consists of three deep-space communications facilities placed approximately 120 degrees apart around the world: at Goldstone, in California's Mojave Desert; near Madrid, Spain; and near Canberra, Australia. This strategic placement permits constant observation of spacecraft as the Earth rotates, and helps to make the DSN the largest and most sensitive scientific telecommunications system in the world.

So we know that we have a three-way network. The Curiosity rover has an onboard power source and radio, which it can use to send radio signals out. Those radio signals are received by the Mars Reconnaisance Orbiter (MRO) which is orbiting Mars. The MRO satellite then uses its own UHF antenna to relay the signal towards earth. The DSN receivers on Earth then receive the signal generated by the satellite. This video provides a nice illustration of how the process works.

NASA provides more details (and another video!) on the communication process on the pages below:

Specifically, during the landing, the DSN radio antennas in Canberra, Australia were the ones receiving the signal. Being that Mars is about 150 million miles from Earth, it's pretty amazing that the radio signals only take about 14 minutes to travel from start to finish!

About the author: Ben Bakelaar is the Library Systems Administrator and has been working in the field of information technology since 2001. However, he was online long before that, going back to the Internet in 1995, AOL in the early 90s, and BBS's before that. He once racked up a $500 monthly phone bill back when telephone companies charged for calls between area codes, a fact easily lost on a 10 year old.